1. Field of the Invention
The present invention relates to a hydraulic circuit for controlling the oil pressure supplied to the automatic transmission of a vehicle having an automatic engine-stop system, in particular, to a hydraulic circuit for quickly supplying the desired oil pressure to the automatic transmission.
2. Description of the Related Art
Conventionally, vehicles having an automatic engine-stop system are known, wherein the engine is stopped according to the driving conditions of the vehicle, and the engine is restarted when specific conditions are satisfied. In such vehicles, fuel consumption can be reduced by suitably stopping the engine. However, if the automatic engine-stop system is applied to vehicles having an automatic transmission, the oil-pressure pump is also stopped together with the engine; thus, it is necessary to maintain the oil pressure controlled by a hydraulic circuit of the automatic transmission.
Japanese Unexamined Patent Application, First Publication, No. Hei 10-324177 discloses an example of the hydraulic circuit for controlling the oil pressure supplied to the automatic transmission of a vehicle having the automatic engine-stop system.
The disclosed vehicle is a hybrid vehicle which can be driven by suitably using an engine, a first motor/generator, and a second motor/generator. The disclosed system comprises the second motor/generator for generating creep during the driving of the vehicle, an automatic transmission coupled with the engine via a torque converter, a first oil-pressure pump driven by the engine, a manual valve, and a second oil-pressure generating means which can supply an oil pressure by which the forward and backward clutches are set in the state immediately before the engagement. As shown in FIG. 8, the second oil-pressure generating means 50 comprises a second oil-pressure pump 52 driven by an electric motor 51, a first check valve 54 for restricting the flow from the manual valve 53 to the second oil-pressure pump 52, a relief valve 55, and a second check valve 57 for restricting the flow from the manual valve 53 to the first oil-pressure pump 56. In FIG. 8, reference symbol E indicates an engine, reference numeral 58 indicates a forward clutch, reference numeral 58 indicates a backward clutch 59, reference numeral 60 indicates hydraulic equipment, and reference numeral 61 indicates a first oil-pressure generating means 61.
However, in the above conventional technique, the second check valve 57 is necessary even in the most simplified structure (as shown above) employing a second oil-pressure generating source. That is, while the engine E is stopped, the second check valve 57 is necessary for preventing the oil pressure from acting on the first oil-pressure generating means 61 if hydraulic oil is supplied from the second oil-pressure generating means 50 to manual valve 53.
Therefore, in order to manufacture a hybrid vehicle having the above-explained structure, the second check valve 57 is necessary in the hydraulic circuit of the automatic transmission of the first oil-pressure generating means 61; thus, presently available (or known) automatic transmissions cannot be used as they are, and must be modified, thereby increasing the necessary cost.
Accordingly, an improved structure without the above second check valve is required in which a presently available automatic transmission can be used as it is.
In consideration of the above circumstances, an objective of the present invention is to provide a hydraulic circuit for controlling the oil pressure supplied to the automatic transmission of a vehicle having an automatic engine-stop system, by which (i) the rise speed of the oil pressure for driving the automatic transmission can be increased when the engine is restarted, (ii) the delay of the response for starting the vehicle can be decreased, and (iii) the hydraulic circuit of a presently available automatic transmission can be used.
Therefore, the present invention provides a hydraulic circuit for controlling the oil pressure supplied to an automatic transmission of a vehicle which has a mechanical oil pump, driven by an engine, for supplying hydraulic oil to the automatic transmission and which has an automatic engine-stop system, wherein:
a bypass passage for connecting the suction side and the supply side of the mechanical oil pump is provided; and
an electric oil pump is connected to the bypass passage in a manner such that the mechanical oil pump and the electric oil pump are arranged in parallel.
According to the above structure, while the engine is stopped, the electric oil pump can be operated so as to fill the oil path of the automatic transmission with hydraulic oil. Therefore, it is possible to prevent a delay in the rise of the oil pressure when the engine is restarted, and to prevent a delay of the response for starting the vehicle.
The hydraulic circuit may comprise:
a check valve, inserted in the bypass passage at the supply side of the electric oil pump, for preventing back flow of the hydraulic oil from the mechanical oil pump to the electric oil pump; and
a first pressure adjusting device (such as a relief valve), provided between the check valve and the electric oil pump, for adjusting a discharge pressure of the electric oil pump.
According to this structure, it is possible to prevent back flow of the hydraulic oil from the mechanical oil pump to the electric oil pump side of the hydraulic circuit while the mechanical oil pump is operated. According to the first pressure adjusting device, it is possible to protect the electric oil pump side of the hydraulic circuit. Therefore, it is possible to prevent the electric oil pump from being damaged.
The hydraulic circuit may further comprise second pressure adjusting device (such as a relief valve) for adjusting the discharge pressure of the electric oil pump, where the set pressure of the first pressure adjusting device is smaller than the set pressure of the second pressure adjusting device.
According to this structure, it is possible to prevent the oil pressure, which is generated from the electric oil pump side of the hydraulic circuit, from discharging from the second pressure adjusting device at the mechanical oil pump side. Therefore, the set pressure of the first pressure adjusting device can be small, and the pumping operation of the electric oil pump can be decreased.
Typically, the bypass passage, the electric oil pump, the check valve, and the first pressure adjusting device are added and attached to the oil path as a unit. Accordingly, in the manufacturing process, the present hydraulic circuit can be easily attached to a presently available mass-produced automatic transmission having a simple structure, thereby decreasing the manufacturing cost.
Preferably, the electric oil pump is activated according to a command for stopping the engine, while the electric oil pump is stopped after the engine is restarted and a predetermined time has elapsed. Accordingly, the driving time of the electric oil pump can be minimized. Therefore, the electric oil pump is not operated unnecessarily, so that the power consumption can be reduced and the durability of the electric oil pump can be improved.
The present invention also provides an oil-pressure control system for controlling a hydraulic circuit as explained above, the system comprising:
an electric oil pump controlling section (for example, motor ECU 11 in the embodiments) for activating the electric oil pump if the section receives an engine stop command for stopping the engine (refer to step S43 in the embodiments), and stopping the electric oil pump if the section receives an engine start command for restarting the engine (refer to step S42 in the embodiments), wherein the electric oil pump controlling section stops the electric oil pump when a predetermined time has elapsed after the engine restart.
The present invention also provides an oil-pressure control method for controlling a hydraulic circuit as explained above, the method comprising the step of:
activating the electric oil pump if an engine stop command for stopping the engine is received, and stopping the electric oil pump if an engine start command for restarting the engine is received, wherein the electric oil pump is stopped when a predetermined time has elapsed after the engine restart.
Accordingly, the operation of the electric oil pump can be stopped when a predetermined time has elapsed after the engine restart, and it is possible to minimize the operation time of the electric oil pump. Therefore, no unnecessary operation of the electric oil pump is performed, and thus power consumption can be reduced and the durability of the electric oil pump can be improved.
The present invention also provides an oil-pressure control system for controlling a hydraulic circuit as explained above, the system comprising:
an electric oil pump controlling section for activating the electric oil pump if the section receives an engine stop command for stopping the engine (refer to step S60 in the embodiments), and stopping the electric oil pump if the section receives an engine start command for restarting the engine (refer to step S59 in the embodiments), wherein after the engine restart, the electric oil pump controlling section determines whether the combustion in the engine has reached a specific maximum level, and stops the electric oil pump when it is determined that the combustion in the engine has reached the specific maximum level.
The present invention also provides an oil-pressure control method for controlling a hydraulic circuit as explained above, the method comprising the step of:
activating the electric oil pump if an engine stop command for stopping the engine is received, and stopping the electric oil pump if an engine start command for restarting the engine is received, wherein after the engine restart, it is determined whether the combustion in the engine has reached a specific maximum level, and the electric oil pump is stopped when it is determined that the combustion in the engine has reached the specific maximum level.
Accordingly, the operation of the electric oil pump can be stopped when it is determined that the combustion in the engine has reached the specific maximum level; thus, it is possible to minimize the operation time of the electric oil pump. Therefore, also in this case, no unnecessary operation of the electric oil pump is performed, and thus power consumption can be reduced and the durability of the electric oil pump can be improved.